High Concentrations Of Heavy Metals Research Articles

Progress and Challenges of Biological Leaching of Heavy Metal in Coal Ash from a Power Plant

Bioleaching is a technique for reducing the heavy metal content of coal ash by using bacteria, fungi, or yeast. Previous studies in heavy metal bioleaching of coal ash discussed the factors affecting the process, but as yet there is little information on the challenges of using microorganisms. Therefore, this study aimed to obtain comprehensive information regarding the use of microorganisms in heavy metal bioleaching. Heavy metal concentrations in coal ash are low, and the metals are diverse. The components of coal ash are complexes that cannot leach certain heavy metals according to previous studies. These low concentrations and complex components make it difficult to investigate the bioleaching mechanism. The combination of biological and chemical interactions involves various components in this system. The high concentration of iron and heavy metal leached could be toxic for microorganisms. The process is influenced by several factors, such as particle size, pH, and pulp density. Most heavy metal bioleaching studies on coal ash have been conducted on a small scale to control conditions affecting the process. Bioleaching kinetics in coal is a liquid-solid reaction that can be represented by the shrinking core model, which was mainly used in this study.

Effectiveness of bio- phytoremediation on heavy metal contaminated soils: A review

The need to restore the environment contaminated with heavy metals to its original ornear original status has become necessary due to the harm high concentration of heavy metals cause to the environment and the food chain. In this review, different remediation approach was considered, their merits and short coming. Focus was more on bio-phytoremediation: use of some selected plants and micro-organisms to decontaminate heavy metals from contaminated sites. . Differentplant species especially hyper accumulative plants were used to decontaminate heavy metals from contaminated site. Vetiver grass (Vetiveriazizanioides) was more effective among all the plant species used. It is environmentally friendly and cost effective. Its ability to accumulate and uptake heavy metals from the soil and translocate same to the shoot was high. Combination of both plants and micro-organisms proved to be more effective with a faster result in remediating a heavy metal polluted soil. Amendment of the soil with organic manures significantly increased the percentage of heavy metals removed from the soil and reduced the uptake of contaminants (heavy metals) from the plant tissues.

Investigations Concerning Heavy Metals Dynamics in Reynoutria japonica Houtt.-Soil Interactions.

Reynoutria japonica Houtt (RJ) is an extremely invasive plant species, found nowadays in a wide range of habitats, including those polluted with heavy metals (HM). The aim of this study was to investigate HM dynamics in RJ-soil interactions in five habitats historically polluted with HM located in Baia Mare city, Romania. The concentrations of major metal elements (Cd, Cu, Pb, Zn) in plant tissues (roots, stems, leaves) and soil samples collected from the study sites were analyzed via portable ED-XRF spectroscopy (converted), and the translocation factor (TF) and bioconcentration factor (BCF) were calculated. The mean values of HM in soil samples collected from the study sites exceeded the threshold limit values established by Romanian legislation. Generally, the highest concentration of Cd was recorded in the above-ground part of the plant (stem and leaves), while for Cu, Pb and Zn, the highest values (with few exceptions) were recorded in the root. The metal transfer was highly effective from soil to RJ, such that all four of the HM studied exceeded the normal range of metals in a plant. Analysis of metal concentrations in plant tissues showed an efficient movement of Cd and Zn to the above-ground parts of the plant, a tendency particularly pronounced in the case of Cd (TF and BCF > 1), while Pb was the least bioaccumulated HM. It may be concluded that RJ is able to tolerate high concentrations of HM, being a good phytoextractor for Cd and Zn.

Extraction of Humic Acids from Lignite and Its Use as a Biochar Activator.

Current research focuses on extracting humic acid (HA) compounds from low-rank coals to obtain high value-added products. In this study, HAs with high purity and low heavy metal content were obtained from lignite by combining acid pretreatment with hydrothermal treatment. Scanning electron microscopy, elemental analysis (EA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to analyze raw lignite and HAs. The effects of acid and hydrothermal treatments on the inorganic elements, functional groups, and yield of HAs were examined. The results showed that acid treatment reduced the ash content of lignite from 20 to 9%, and hydrothermal treatment increased the yield of HAs from 36 to 68%. The chemical properties of HAs exhibited an increase in molecular weight and improved aromaticity after acid and hydrothermal treatments. The results of ICP-OES analysis suggested that the combined method of acid and hydrothermal treatments resulted in a significant reduction of heavy metal elements in HAs. FTIR analysis confirmed the results and demonstrated that the extracted HA from nitric acid pretreated and hydrothermal generation of lignite PHA was rich in carboxyl and phenolic functional groups. PHA was applied to biochar as an activator for the adsorption of heavy metal ions. The experimental results showed that PHA was successfully loaded onto biochar and introduced a large number of functional groups, and the adsorption capacity of the modified biochar for Pb2+ was effectively improved.

Enhanced electrokinetic remediation by magnetic induction for the treatment of co-contaminated soil

The electroplating industry site is an important reservoir of per- and poly-fluoroalkyl substances (PFASs) and heavy metals. In this work, a novel electrokinetic in-situ chemical oxidation system was established to restore an actual soil co-contaminated with high concentrations of heavy metals (Cr, Cu, Zn and Ni) and PFASs. Potassium persulfate (PS, K2S2O8) and industrial waste steel slag were used as the oxidant and activator, respectively. The steel slag was evenly added in the soil, while PS was dosed in the cathode chamber. Citric acid fermentation broth produced by Aspergillus niger was added in the anode chamber to act as the metal chelator. A periodic alternating magnetic field was employed to enhance the catalytic performance of steel slag for PS. After 15-day treatment, 86.7% of PFASs and 87.2% of heavy metals were removed without PFASs accumulation in the electrolyte, with a defluorination percentage of 79.2%. The remediated soil had no phytotoxicity for wheat seed growth based on 7-day cultivation results. The quality of remediated soil could reach the national Class II criteria for residential use. Electron paramagnetic resonance spectroscopy analysis demonstrated that SO4•– and •OH were the major oxidative radicals responsible for PFASs degradation. Adding steel slag in the soil performed better than that in the cathode chamber based on pollutant removal and alleviating soil acidification. Magnetic induction could enhance PS activation by promote the corrosion of steel slag and thermal activation, thus increasing electrical current and electroosmotic flow, enhancing the transport of citric acid and PS, significantly improving the removal efficiency of heavy metals and PFASs.

Physicochemical Technique in Municipal Solid Waste (MSW) Landfill Leachate Remediation: A Review

Leachate generation is among the main challenging issues that landfill operators must handle. Leachate is created when decomposed materials and rainwater pass through the waste. Leachate carries many harmful pollutants, with high concentrations of BOD, COD, colour, heavy metals, ammoniacal nitrogen (NH3-N), and other organic and inorganic pollutants. Among them, COD, colour, and NH3-N are difficult to be completely eliminated, especially with a single treatment. They should be handled by appropriate treatment facilities before being safely released into the environment. Leachate remediation varies based on its properties, the costs of operation and capital expenditures, as well as the rules and regulations. Up until now, much scientific and engineering attention was given to the development of comprehensive solutions to leachate-related issues. The solutions normally demand a multi-stage treatment, commonly in the form of biological, chemical, and physical sequences. This review paper discussed the use of contemporary techniques to remediate landfill leachate with an emphasis on concentrated COD, colour, and NH3-N levels with low biodegradability that is normally present in old landfill or dumping grounds in developing countries. A semi-aerobic type of landfill design was also discussed, as this concept is potentially sustainable compared to others. Some of the challenges and future prospects were also recommended, especially for the case of Malaysia. This may represent landfills or dumpsites in other developing countries with the same characteristics.

The carrying capacity of estuarine mangroves in maintaining the coastal urban environmental health of Southeast Sulawesi, Indonesia

This study aims to elucidate the carrying capacity of estuarine mangroves in Southeast Sulawesi, to maintain environmental health of its coastal cities. The concentrations of mercury (Hg), Copper (Cu), Manganese (Mn), Lead (Pb), Zinc (Zn), and Nickel (Ni) were analyzed in sediments and mangrove tissues samples from Kendari bay and Tinanggea estuaries. This was followed by the determination of translocation and bioaccumulation factors, as well as the total accumulation of heavy metals on a landscape level. The results showed that the sediment in Kendari Bay had higher heavy metal concentrations than in Tinanggea, indicating the anthropogenic impact of the highly populated city of Kendari. Moreover, the roots and stems of mangroves had higher heavy metal concentrations than the leaves. Overall, the Bioconcentration Factors (BCF) of Hg, Cu, Mn, Pb and Zn metals were >1, indicating that estuarine mangroves have a higher phytoremediation capacity for heavy metals. Estuarine mangrove biomass also enables the high accumulation of heavy metals in both Kendari bay and Tinanggea, signifying the greater phytoremediation potential of urban estuarine mangroves. Based on these findings, the study supports the conservation and management of mangroves in urban estuaries to maintain the environmental health of coastal cities.

Accumulation and human health risk assessment of trace elements in two fish species, Cirrhinus mrigala and Oreochromis niloticus, at Tarukri Drain, District Rahimyar Khan, Punjab, Pakistan.

The toxic discharge of heavy metals into the water affects the aquatic ecosystem as well as the human population interacting with it because of their toxicity, bioaccumulation, long persistence, and transfer through the food chain. Thus, it is very important to conduct studies to determine the level of heavy metal pollution in order to better control, manage, and preserve the pollution of aquatic ecosystems. This study assessed heavy metal contamination in fish and its associated health risk to the population around the Tarukri Drain, Punjab, Pakistan. Two fish species (Oreochromis niloticus and Cirrhinus mrigala) were collected from three different sites in two different seasons. Collected fish were analyzed for cadmium (Cd), iron (Fe), lead (Pb), nickel (Ni), and zinc (Zn) accumulation using atomic absorption spectrometer (AAS). Furthermore, the human health risks associated with the consumption of affected fish were also assessed. Target hazardous quotient for seasonal consumers was between 0.12, - 1.58 × 10-4, and 0.54 - 3.28 × 10-4 (mg/kg) in O. niloticus and C. mrigala, respectively. While for regular consumers it was between 0.28-3.71 × 10-4 and 1.27-7.68 × 10-4 (mg/kg) in O. niloticus and C. mrigala respectively for the studied heavy metals. Fish sampled from Sadiqabad contained the highest concentration of heavy metals. The analysis of fish organs (kidney, liver, and muscles) showed heavy metal accumulation in the order of kidney > liver > muscles (p < 0.00). The obtained results showed that heavy metal contaminations in both fish species were within the permissible limits recommended by the World Health Organization (WHO). Both sampling seasons (i.e., summer and winter) showed a non-significant difference in heavy metal concentration. The calculated total target hazardous quotient across all heavy metals remained < 1 with only one exception. The carcinogenic risk assessment of heavy metals showed a non-significant effect in both fish species.

Providencia alcalifaciens—Assisted Bioremediation of Chromium-Contaminated Groundwater: A Computational Study

In Saudi Arabia, seawater desalination is the primary source of acquiring freshwater, and groundwater contains a high concentration of toxic heavy metals. Chromium (Cr) is one of the heavy metals that is widely distributed in the environment, particularly in the groundwater of Madinah. Diverse techniques are employed to eliminate the toxicity of heavy metals from the environment, but, lately, the focus has shifted to biological remediation systems, due to their higher removal efficiencies, lower costs, and more ecologically benign characteristics than the conventional methods. Providencia bacteria engage in a variety of adsorption processes to interact with heavy metals. In this study, we aim to investigate the role of potential active site residues in the bioengineering of chromate reductase (ChrR) from Providencia alcalifaciens to reduce the Cr to a lesser toxic form by employing robust computational approaches. This study highlights Cr bioremediation by providing high-quality homology-modeled structures of wild type and mutants and key residues of ChrR for bioengineering to reduce the Cr toxicity in the environment. Glu79 is found to be a key residue for Cr binding. The mutant models of Arg82Cys, Gln126Trp, and Glu144Trp are observed to establish more metallic interactions within the binding pocket of ChrR. In addition, the wild type ChrR (P. alcalifaciens) has been found to be unstable. However, the mutations stabilized the structure by preserving the metallic contacts between the critical amino acid residues of the identified motifs and the Cr(VI). Therefore, the mutants discovered in the study can be taken into account for protein engineering to create reliable and effective enzymes to convert Cr(VI) into a lesser toxic form.

Identification and Characterization of the Determinants of Copper Resistance in the Acidophilic Fungus Acidomyces richmondensis MEY-1 Using the CRISPR/Cas9 System.

Copper (Cu) homeostasis has not been well documented in filamentous fungi, especially extremophiles. One of the main obstacles impeding their characterization is the lack of a powerful genome-editing tool. In this study, we applied a CRISPR/Cas9 system for efficient targeted gene disruption in the acidophilic fungus Acidomyces richmondensis MEY-1, formerly known as Bispora sp. strain MEY-1. Using this system, we investigated the basis of Cu tolerance in strain MEY-1. This strain has extremely high Cu tolerance among filamentous fungi, and the transcription factor ArAceA (A. richmondensis AceA) has been shown to be involved in this process. The ArAceA deletion mutant (ΔArAceA) exhibits specific growth defects at Cu concentrations of ≥10 mM and is transcriptionally more sensitive to Cu than the wild-type strain. In addition, the putative metallothionein ArCrdA was involved in Cu tolerance only under high Cu concentrations. MEY-1 has no Aspergillus nidulans CrpA homologs, which are targets of AceA-like transcription factors and play a role in Cu tolerance. Instead, we identified the Cu-transporting P-type ATPase ArYgA, homologous to A. nidulans YgA, which was involved in pigmentation rather than Cu tolerance. When the ΔArYgA mutant was grown on medium supplemented with Cu ions, the black color was completely restored. The lack of CrpA homologs in A. richmondensis MEY-1 and its high tolerance to Cu suggest that a novel Cu detoxification mechanism differing from the AceA-CrpA axis exists. IMPORTANCE Filamentous fungi are widely distributed worldwide and play an important ecological role as decomposers. However, the mechanisms of their adaptability to various environments are not fully understood. Various extremely acidophilic filamentous fungi have been isolated from acidic mine drainage (AMD) with extremely low pH and high heavy metal and sulfate concentrations, including A. richmondensis. The lack of genetic engineering tools, particularly genome-editing tools, hinders the study of these acidophilic and heavy metal-resistant fungi at the molecular level. Here, we first applied a CRISPR/Cas9-mediated gene-editing system to A. richmondensis MEY-1. Using this system, we identified and characterized the determinants of Cu resistance in A. richmondensis MEY-1. The conserved roles of the Cu-binding transcription factor ArAceA in Cu tolerance and the Cu-transporting P-type ATPase ArYgA in the Cu-dependent production of pigment were confirmed. Our findings provide insights into the molecular basis of Cu tolerance in the acidophilic fungus A. richmondensis MEY-1. Furthermore, the CRISPR/Cas9 system used here would be a powerful tool for studies of the mechanisms of adaptability of acidophilic fungi to extreme environments.

Early immune response of neuronal cells (U87) to heavy metal Cd or Pb exposure.

Heavy metals such as lead (Pb) and cadmium (Cd) exist as particulate matter (PM) in the air and can cause biological damage to cells, animals, and humans. However, the mechanism underlying the toxic effects of heavy metals on nerve cells has not yet been completely identified. Glioma is the most common and fatal tumor in the central nervous system; the U87 human glioblastoma cell line is commonly used when researching brain cancer, including aggressive malignant gliomas. Therefore, in this study, cell viability, cytotoxicity, and interleukin-6 (IL-6) levels were analyzed to confirm the effect of Cd and Pb exposure on U87 cells. On confirming the absence of significant effects on cell viability at low concentrations of heavy metals, Cd and Pb exposure had no effect on lactic acid dehydrogenase (LDH) activity at the concentrations (1 μg/L, 30 μg/L, and 1 mg/L) used in this study, and there was a remarkable effect of Cd and Pb exposure on the inflammatory response of these cells. Our findings provide a basis for future research elucidating the effects of heavy metal exposure on cellular pathology. Systematic studies with higher heavy metal concentrations and precision are warranted to deepen our understanding of the relationship between heavy metal exposure and neuronal responses.

Assessment of the chemical and radiological safety of wild mushrooms and berries growing in the Arkhangelsk region

AIM: To analyze the levels of contamination with heavy metals and radionuclides of wild mushrooms and berries growing in the Arkhangelsk region.&#x0D; METHODS: Data on the content of heavy metals (cadmium, mercury, lead, arsenic) and radionuclides (cesium-137 and strontium-90) in berries and mushrooms were studied in accordance with the protocols of the Agrochemical Service Station Arkhangelskaya and the Center for Hygiene and Epidemiology in the Arkhangelsk Region and the Nenets Autonomous Okrug during the period of 20152021. Total 201 samples of mushrooms and 175 samples of berries were analyzed.&#x0D; RESULTS: The levels of heavy metals did not exceed the maximum permissible concentrations in 94% of the studied samples of mushrooms and 86% of the studied samples of berries. All samples of mushrooms and berries corresponded the hygienic standards for the content of radionuclides. The mean concentrations of mercury (0.013 mg/kg) and cadmium (0.040 mg/kg) in mushrooms were higher than the average concentrations of these metals in berries by 2.1 (p=0.002) and 1.8 times (p 0.001), respectively. At the level of median concentration and 90th percentile, the content of mercury in tubular mushrooms (0.036 and 0.047 mg/kg, respectively) was 3.2 times higher in comparison to plate mushrooms (p=0.003). The highest content of arsenic (0.067 and 0.24 mg/kg, respectively) and lead (0.088 and 0.15 mg/kg) were found in the berries of the large-sized shrubs at the level of average concentration and the 90th percentile compared to other shrub species, but the differences were not statistically significant.&#x0D; CONCLUSION: The comparative analysis concluded that although mushrooms and berries from the Arkhangelsk region contain low concentrations of heavy metals and radionuclides, mushrooms tend to accumulate higher concentration of heavy metals and radionuclides in comparison to berries.

Effects of Heavy Metals on the Yield of Essential Oil From Vetiver Grass Cultivated in Mine Tailings Amended With EDTA and Arbuscular Mycorrhizal Fungi

Background/Objective: Vetiver grass (Vetiveria zizanioides (L.) Nash. Syn. Chrysopogon zizanioides (L.) Roberty; family Poaceae) is well-known for producing essential oil that is commonly used in premier perfumery, food, and pharmaceutical industries. The quality of essential oil produced should be assessed before application in production of various products. Methods/Results: In this study, the yield of essential oil extracted from vetiver grass found in Botswana was assessed after cultivation in mine tailings. The respective influence of chelating agents and microbes such as ethylene diamine tetra-acetic acid (EDTA) and arbuscular mycorrhizal fungi (AMF) on the yield of essential oils was also evaluated. Results obtained showed that vetiver grass grown in mine tailings produced more essential oils compared to unpolluted soils. Vetiver grass grown on sterilized soils yielded only 0.26% of essential oils compared to 0.86% of that cultivated in mine tailings. Furthermore, essential oil yield was increased in soil amended with EDTA (0.95%) and after inoculation with AMF (0.89%). Addition of EDTA and AMF enhanced the uptake of heavy metals by vetiver grass and increased heavy metal stress and thereby making vetiver grass release secondary metabolites in the form of essential oils. It is important to note that even though the mine tailings accumulated high concentrations of heavy metals (As: 47.31 ± 1.40, Cu: 1632.24 ± 38.20, Mn: 402.68 ± 18.21, Ni: 728.26 ± 46.20, Pb: 41.26 ± 5.38, and Zn: 103.97 ± 5.34), very low concentrations of metals were detected in essential oils extracts. Conclusion: This study indicates the ability of vetiver grass to produce more essential oil under heavy metal stress making it useful for both essential oil production and important candidate for phytoremediation.

Application of Sulfate-reducing Bacteria in Bioremediation from Heavy Metals and Metalloids (Review)

Pollution of the environment with heavy metals, metalloids and radionuclides is a global problem that seriously affects the state of the biosphere. In particular, chromium compounds have a toxic, mutagenic and carcinogenic effect. The main principle of purification of anthropogenic and natural ecosystems from chromates is the reduction of Cr(VI) to Cr(III), the salts of which are significantly less toxic and insoluble. However, currently used electrochemical and ion-exchange cleaning methods are quite expensive and require the use of special reagents. At the same time, sulfate-reducing bacteria (SRB) are of particular interest for bioremediation of this kind, since many of them are very resistant to high concentrations of heavy metals and are able to effectively reduce them in the presence of hydrogen as an electron donor. The review summarizes known data on the interaction of heavy metals, metalloids and radionuclides with SRB. The features of the metabolism of these microorganisms, leading to intracellular accumulation of heavy metals and metalloids, are considered. Complex and finely regulated enzymatic mechanisms for the reduction of toxic metals (using various cytochromes, hydrogenases, oxidoreductases, highly specific metal reductases, and thioredoxin/thioredoxin-reductase systems), as well as the possibility of using immobilized cells and biofilms of SRB in the effective bioremediation of natural waters, soils, and industrial effluents, are described.

Hydrodesulphurisation of Petroleum Coke

Hydrodesulphurisation in a fluidized bed offers the most attractive process for the desulphurisation of petroleum coke. Results of coke hydrodesulphurisation clearly indicate that the rate of sulphur removal is greatest at about 1100 K. The hydrodesulphurisation process is particularly effective with cokes of high sulphur content and high ash and heavy metals content, as at temperatures less than 1100 K the adverse effects of high ash and heavy metals content on desulphurisation is largely avoided. The process leads in general to increased porosity, density and surface area and improved reactivity. These properties are dependent on the sulphur concentration. The greater the amount of sulphur removed, the greater the structural changes expected in the coke treated. The weight loss is less than 10%.

Micro-Evolutionary Processes in Armeria maritima at Metalliferous Sites.

Tolerance to heavy metals in plants is a model process used to study adaptations to extremely unfavorable environments. One species capable of colonizing areas with high contents of heavy metals is Armeria maritima (Mill.) Wild. A. maritima plants growing in metalliferous areas differ in their morphological features and tolerance levels to heavy metals compared to individuals of the same species growing in non-metalliferous areas. The A. maritima adaptations to heavy metals occur at the organismal, tissue, and cellular levels (e.g., the retention of metals in roots, enrichment of the oldest leaves with metals, accumulation of metals in trichomes, and excretion of metals by salt glands of leaf epidermis). This species also undergoes physiological and biochemical adaptations (e.g., the accumulation of metals in vacuoles of the root's tannic cells and secretion of such compounds as glutathione, organic acids, or HSP17). This work reviews the current knowledge on A. maritima adaptations to heavy metals occurring in zinc-lead waste heaps and the species' genetic variation from exposure to such habitats. A. maritima is an excellent example of microevolution processes in plants inhabiting anthropogenically changed areas.

Assessment of heavy metals in water, fish tissues and soil from selected fish farms in Ekiti State, Nigeria

Heavy metals were determined in samples of fish tissues, soil, and water from nine randomly selected fish farms based on production facility (earthen pond) in the Ekiti Central (EC), Ekiti North (EN) and Ekiti South (ES) senatorial districts of Ekiti state. Fresh fish samples were collected and tissues from the dorsal area were used for analysis. Soil samples were collected using a soil auger, air-dried and stored in a sterile and well-labeled polythene bag. The water samples were collected using sterile bottles (2L) and labeled. After digestion of samples, Cadmium (Cd), Copper (Co), Chromium (Ch), Lead (Pb) and Zinc (Zn) were analyzed using Atomic Absorption Spectrometer (AAS). The levels of Co, Cd and Pb which are disastrous to fish species were observed to be elevated while Zn and Cu were observed to accumulate in the fish tissues. It was revealed that the heavy metals concentration across the districts was higher when compared with recommended standards. This suggests a dire need for intervention in controlling water pollution which is posed by anthropogenic activities in the state. It is recommended that there should be a reduction in the use of chemicals with high concentrations of heavy metals which is a significant source of pollution in the environment.

Fixed-bed columns mathematical modeling for selective nickel and copper recovery from industrial spent acids by chelating resins

Spent acid streams generated in industry containing high concentrations of heavy metals are potential secondary sources of raw materials. Chelating resins are excellent candidates to recover valuable metals from complex mixtures at very low pH conditions. In particular, previous works reported high recoveries of nickel and copper from real industrial acids (3400 mg Cu2+ L−1, 8700 mg Ni2+ L−1 and 24000 mg Fe L−1) using commercial bis-picolyamine (BPA)-based resins. In this work, adsorption and desorption using two in-series fixed-bed columns with BPA resins have been proposed to carry out the selective and independent separation and recovery of nickel and copper. Under the selected operating conditions, it was possible to recover 90% of the copper and 80% of the nickel present in the problem solution. A mathematical model based on mass transfer was developed in order to describe the adsorption and desorption stages. Adsorption chemical reactions were modeled as equilibrium reactions, fitting to Langmuir’s and Freundlich’s isotherms for copper and nickel respectively. The chemical reactions for both metals in desorption fitted into first order reactions. Finally, the kinetic constants kde=0.81 kgdryresin L−1 h−1 for copper and kde=1.10 kgdryresin L−1 h−1 for nickel were estimated using the software Aspen Custom modeler. The predicted values agreed with the experimental data.

Shoot-root signal circuit: Phytoremediation of heavy metal contaminated soil.

High concentrations of heavy metals in the environment will cause serious harm to ecosystems and human health. It is urgent to develop effective methods to control soil heavy metal pollution. Phytoremediation has advantages and potential for soil heavy metal pollution control. However, the current hyperaccumulators have the disadvantages of poor environmental adaptability, single enrichment species and small biomass. Based on the concept of modularity, synthetic biology makes it possible to design a wide range of organisms. In this paper, a comprehensive strategy of "microbial biosensor detection - phytoremediation - heavy metal recovery" for soil heavy metal pollution control was proposed, and the required steps were modified by using synthetic biology methods. This paper summarizes the new experimental methods that promote the discovery of synthetic biological elements and the construction of circuits, and combs the methods of producing transgenic plants to facilitate the transformation of constructed synthetic biological vectors. Finally, the problems that should be paid more attention to in the remediation of soil heavy metal pollution based on synthetic biology were discussed.

Quantifying excess heavy metal concentrations in drainage basins using conservative mixing models

High concentrations of heavy metals and other pollutants in river sediments can have detrimental effects on the ecosystem and humans. The composition of river sediments throughout drainage basins therefore provides important information for environmental monitoring. An obvious first step for using river sediment compositions for monitoring is to quantify natural baseline concentrations. Once baselines have been quantified, it is straightforward to compare them to observations to identify excesses generated by, for example, anthropogenic inputs. In this study a new strategy for mapping element concentrations along rivers from discrete geochemical observations upstream is presented. We demonstrate our approach in a case study of the Clyde drainage basin in western Scotland, UK. First, continuous baselines are generated using simple forward models that conservatively mix source region concentrations along drainage networks. 1185 measurements of elemental concentrations from first-order streams are used to parameterise the source region. The calculated baselines are then compared to concentrations measured at 60 localities along the main channel of the Clyde river. For a range of major and trace elements (e.g., Mg, Sr, K, Mn), the downstream observations are in close agreement with baseline concentrations predicted by conservative mixing models. However, some heavy metal concentrations (Pb, Cu, Zn) tend to exceed predicted baseline concentrations. Therefore, the second part of our approach calculates element concentrations in source areas required to match the observed Pb, Cu and Zn concentrations measured along the river. An inverse approach is used to ‘unmix’ the observed concentrations utilising, again, a conservative mixing model. Model resolution is determined by the spatial distribution of the data. Resultant calculated natural baselines and heavy metal concentrations along the river can easily be compared to estimate excesses. We tentatively suggest that anthropogenic input to sediment composition along the river is equivalent to annual fluxes of 9.7, 1.5 and 5.7 t (106 g) of Pb, Cu and Zn, respectively.